When drying wood in a wood drying kiln, an end-point moisture content of 5% to 20% is normally required. Traditional methods of measuring the moisture content of wood, whilst reasonably accurate towards the end-point moisture content, become less accurate at higher values of the moisture content. At a moisture content of above 30%, the traditional methods become completely unreliable.
For the proper control of the environment in which wood is dried, for example, in a wood-drying kiln, it is important for the moisture content of the wood to be known accurately while the moisture content is still relatively high, e.g. above 30%. If the moisture content is accurately known at these relatively high values it becomes possible to accelerate the drying process considerably, without causing undue stresses in the wood.
The complexity of wood is easily under estimated. Wood is highly an-isotropic both in anatomy and by its electrical and dielectric properties. It is a complex composition of air, water cell-wall structure, organic materials such as cellulose, lignin and resins, inorganic salts and ion concentrations. The anatomy is comprised of solid cell-wall structures combined with trachea (tangential hollow tubes) which is either filled with water or air depending on the moisture content (m.c.) of the sample. Furthermore, variations within species is remarkably striking regarding ion-content which translates in conductivity and resistive variations. Species-to-species variations in ion content is even more influential and wide species to species changes in conductivity is experienced. In order to measure the dielectrics of such a complex medium, the influences of each of these components need be addressed before valuable and usable measurements and methods can be devised. The measurement of the dielectric properties of wood is particularly and unexpectedly troublesome as reported in detail in the book by Torgovnikov[C]. (The citations herein identified by upper case letters are o the bibliography at the end of the specification.) Not only is the dielectric highly an-isotropic and grain direction dependent, the unexpected temperature behavior of the conductivity of wood is worth mentioning. It would be expected that wood would have similar characteristics as usual carbon based resistors, which displays a decrease in conductivity with increased temperature (increase in resistance respectively). The conductivity of wood in fact does not follow this trend at all, but rather displays the temperature dependence strikingly similar to a semi-conductor i.e. the conductance increases with increasing temperature. It is clear that if this is not taken into account measuring methods of e.g. capacitance of the wood-dielectric will fail at elevated temperatures as large errors will be introduced. This particular fact resulted in several measurement systems to fail in industry for obvious reasons James[R]. To make matters even more troublesome, extremely non-linear anomalies occurs regarding the other relevant dielectric component namely the relative permittivity ∈r also known in layman's terms as the dielectric constant. Since the relative permittivity gives rise to capacitance via the probe geometry and since capacitance will be what is measured, this influence will be discussed in terms of the capacitance but is equally valid for the relative permittivity. Dielectric constant and as a consequence capacitance increases substantially with increase in temperature compared to more homogeneous dielectrics. However, Torgovnikov [C] cites James's results to display the following anomalies. Not only is the relative permittivity and therefore capacitance wildly frequency dependent, it does so in an unexpected manner. Completely dry (bone-dry) wood has a relative permittivity of 4, while water has a relative permittivity of 80. The relative permittivity of water and bone-dry wood is for all purposes frequency independent except for the normal dispersion variations not of relevance here. However, when water and wood is combined i.e. wet wood is measured, we do not obtain the intuitive combined relative permittivity of 84, but instead values are reported by Torgovnikov and James [C] of ∈r=650000 at certain lower frequencies. This is most certainly an anomaly and to date still unexplained and seemingly not challenged however unlikely it seems. Furthermore the relative permittivity and therefore the capacitance increases dramatically with decrease in frequency compared to minimal change in ∈r detected for pure water and bone-dry wood when not in combination over the same frequency range. In addition the loss-tangent tan δ, which is an indication of how lossy a material is in an applied electromagnetic field, also displays curious anomalies generally not expected from dielectric media. Even the most complex composites usually has a loss-tangent, for which each value of loss-tangent only one value of element of composition can be obtained. With wood as dielectric the loss-tangent generally becomes a relation i.e. the loss-tangent plotted against moisture content is that of a bell-curve Torgocvnikov [C] resulting in two moisture contents giving the same loss-tangent reading. This clearly cancels loss-tangent for measurement above f.s.p. in most cases as it results in ambiguity. These complications dwarfs the already significant an-isotropic behavior of ∈r which has different values when the applied electromagnetic field is applied tangential and radially to the wood respectively. The remaining significant behavior of the wood-water relationship is at f.s.p, where free water starts to assemble in the hollow trachea and dissolves salts. These ions then drastically increase the conductivity above f.s.p. to enormous proportions and in effect making any correlation of moisture content above f.s.p. difficult if not impossible. The conductivity of wood therefore becomes an almost constant high value above f.s.p. literally independent of higher moisture contents. The reason for the sudden conductivity increase above f.s.p. is due to the minerals K, P, Al, Fe, Zn, Ca, Mn, Cl, Na and Mg, to name a few which are naturally encountered in wood. The majority of these minerals are dissolved and present in the free water as ions and therefore has a phenomenal influence on conductivity above f.s.p. Below f.s.p. no free water exists and these minerals are then deposited on the cell walls with less influence.
The bounded water (adsorbed water on cell walls) is also changed fundamentally in that the water which is now adsorbed by the cell-walls clearly cannot be rotated easily as a dipole in the applied field. As the wood dries the adsorption to the cell-walls increases giving even more resistance to rotation in the applied electromagnetic field. This results in a curved relationship between ∈r at moisture contents below f.s.p. Above f.s.p. the free water in the hollow trachea are the dominant influence on ∈r and ∈r versus moisture content and the H2O molecules as dipole can easily and unrestrictedly be oriented in the applied electromagnetic field. This is the reason why ∈r is then linear from f.s.p upwards to 200%. This combined then establishes a curve-linear relationship between ∈r and the moisture content as empirically verified by Skaar[F]. It is therefore evident that two “types” of water exists in the wood-water combination and they influence the dielectric properties in a very different way. The list of behavioral anomalies are not exhausted as there are piezzo electrical effects creating electrical impulses during drying due to crystalline structures in the wood and several more which will not be discussed, although further complications arises due to them. Wood rivals if not champions the most complex composite dielectrics, is rich in anomalies and unexpected behavior. These anomalies and properties are crucial to understand why some measuring processes in prior art, when applied to wood, are irrelevant or non-functional and will be referred to in sequel.
Dielectric Model of Wood
It is well known from literature that the sensitivity of inductance to moisture content of wood is negligible. The dielectric for wood would then comprise of the various influences of dielectric constant ∈r and conductivity σ only.
The full dielectric model for wood is displayed in FIG. 1. All the different kinds of polarizations evident for wood are represented by the various capacitances. They are Ce Ca Cd Cv and Cz, effected by electronic, ionic, dipole, inter-facial, electrolytic, polarizations. Rd, Rv, Rz and Rl are the resistances resulting from energy losses at dipole, inter-facial, electrolytic, and resistance related to the direct current, respectively.
The model in FIG. 1 is for analytical purposes and a practical model used in determination of dielectric properties of wood for commercial systems is the Thevenin-Norton, lumped model as in FIG. 2 where the representative dielectric components are now the lumped values Cx and Rx.
In the discussion below, it will be understood that the model as shown in FIG. 2 is used.
As a dielectric, wood is then comprised of physically and chemically inseparable components Rx and Cx combined in parallel to form an impedance. It is of utmost importance to understand that with wood as a dielectric, Rx and Cx cannot be treated as discreet components as one of the components cannot be physically removed from the medium to have only the other to remain and then just decide to measure one but ignore the other.
Correlation with Moisture Content
Several correlations of moisture content in wood are possible and are substantially researched, refereed, published and discussed by researchers in the field of wood-science.
Correlation of the Moisture Content with Conductivity
Conductivity manifests itself by means of resistance measurements and corresponds to conductivity according to the probe geometry used. As the bounded wood-water reaches a saturated state at around f.s.p. (30% m.c.), any moisture content above f.s.p. will result in free water condensing in the trachea. The salts deposited on the cell-walls then dissolves increasing the conductivity radically until a maximum is reached. The graph in FIG. 3 shows that it is not feasible to correlate conductivity with moisture contents above f.s.p. as there is not much resolution. This is the reason why resistive type measuring systems fails to give consistent readings above f.s.p. and can only measure in the shaded area correlation of the moisture content with the loss-tangent (tan δ).
Correlation of Moisture Content with Loss-Tangent
Loss-tangent can be obtained from the conductivity and relative permittivity by means of       tan    ⁢                   ⁢    δ    =            1              ω        ⁢                                   ⁢                  R          x                ⁢                  C          x                      .  It displays less of the restrictions of conductivity above f.s.p. but it is ambiguous as for every value of tan δ there exists two moisture contents. It is therefore usually only restricted to measurements below f.s.p. Since it is dependent on resistance, the values above f.s.p. will inherit the instabilities of resistance above f.s.p. due to hysteresis effects. FIG. 4 show how moisture content varies with loss tangent correlation of the moisture content with the dielectric constantCorrelation of the Moisture Content with Dielectric Constant ∈r 
This correlation manifests itself in capacitance measurements where capacitance is proportional to ∈r by means of the probe geometry. Therefore all pure or exact capacitance measurements must correlate to moisture content according to the curve-linear graph such as in the FIG. 5.
As can be seen, there is no difficulty correlating pure capacitance with moisture contents above f.s.p. and the full range of moisture contents are available. These curves have been obtained and verified by Skaar, Uyemura, James at high frequencies and others under controlled conditions eliminating conductive influences. At lower frequencies capacitance has less influence on the impedance and conductance becomes dominant making it more difficult to obtain the same trend as the pure capacitance becomes obscured.
Definition of and Comparisons Between Resistive and Capacitive Sensors
It is of importance to focus on the two dielectric measurement principles namely “Capacitance” and “Conductivity” of the wood sample as is clear from the above descriptive of the dielectric model of wood. The classification of all the type of dielectric moisture measurement principles is now established.                It is clear that a measurement principle which claims to be a capacitance meter must be able to single out and measure only the capacitance Cx in FIG. 1 and be generally insensitive to changes in Rx.        Likewise, a measurement principle which claims to be a resistance meter must be able to single out and measure only the resistance Rx in FIG. 2 and be generally insensitive to changes in Cx.        Then, for a measurement principle to claim to be a loss-tangent meter       (                  tan        ⁢                                   ⁢        δ            =              1                  ω          ⁢                                           ⁢                      R            x                    ⁢                      C            x                                )    ,it must be clear that the meter combines the Rx and Cx components in such a way as to represent loss-tangent closely.        Any measurement principle unable to separate the components Rx and Cx in FIG. 1 will therefore be a non-linear convolution of dielectric properties and no fundamental information regarding Rx and Cx can be extracted. The output of such measurement is therefore some convoluted indication of the influences of both Rx and Cx. This measurement type will be referred to as of “convoluted” type hereinafter.        Measurement methods which can measure and identify Rx, Cx and tan δ accurately and independently will be described as “Pure-measurements” hereinafter.        Furthermore, if a single measurement principle can obtain all the separate dielectric properties at once and in real time, it will be called “real-time measurements” hereinafter.        
It is important to distinguish between the type of cited measurement principles in the prior-art in order understand and appreciate the differences between the prior art when applied to wood as dielectric medium.
State of the Art
Ahtianien [N] discloses a method by which he claims to measure capacitance of an organic material as dielectric e.g. grain. The circuit proposed there, measures only the amplitude of the alternating voltage over a capacitance C, and then rectifies it by an ideal solid state rectifier. The circuit is analyzed as follows.
The oscillator generates a real valued alternating voltage Vo and the voltage across the dielectric to be measured is defined as Vd. Since the input impedance of the operational amplifier is extremely large very little loading or error will be introduced on the dielectric containing C. The circuit will therefore show                 V      d            =                                  Z          d                                      Z            d                    +                      R            1                              ⁢              V        d                as the output of this circuit. It is clear from the body and specification of the patent that the author defines his model for the dielectric of wheat as that of a capacitance C only. In order to apply and evaluate the method of Ahtianien to wood as a dielectric, we need to replace the Capacitance C representing the dielectric with that of a capacitance in parallel with a resistance to represent wood as shown in FIG. 2. We then analyze the performance of this invention on the model for wood. Since wood as a dielectric is comprised of two physically inseparable components namely Rx and Cx, and since Ahtianien assumes that there are no or negligible influences of Rd present, we will now refer to the situations where Rd is varied. We use published data on the properties of wood to construct an example. From Torgovnikov[C], we obtain tables for dielectric properties of wood at elevated temperatures. Consider the case of density       ρ    =          0.5      ⁡              [                  g                      cm            3                          ]              ,temperature T=90° C. and moisture content m.c.=40%. The dielectric properties listed at these conditions are tan δ=24 and ∈d=221. Assuming the most basic probe setup namely, a parallel plate probe with the mentioned wood-dielectric disposed between it and choosing the area of the plates as ratio to distance between them             A      d        =    1    ,we obtain the capacitance as Cd=∈0 ∈r=1.956 nF, where       ɛ    0    =            8.8510              -        12              ⁡          [              F        m            ]      is the permittivity constant of the free vacuum. A trivial calculation using             tan      ⁢                           ⁢      δ        =                  1                  ω          ⁢                                           ⁢                      R            d                    ⁢                      C            d                              ⁢      yields        ,yields, Rd=339 Ω for wood using the published data.
The percentage error introduced by not considering the resistance in the dielectric for the invention as in [N] is now investigated. Since the dielectric of wood is comprised of a capacitance in parallel with a resistance, we now conclude by considering two cases. The first calculating the output voltage of the circuit as intended by Ahtianien, meaning without the resistance connected in parallel with the capacitor as in his circuit and then repeating the calculation when a resistor is connected in parallel with a capacitor of the same value as the first test. Ahtianien discloses that he chooses R1 for every suitable measuring range by means of choosing it equal to the reactance of the capacitive component. Since we calculated the capacitance from the published data, the value for R1 as required by Ahtianien equates to 8.136 kΩ. By comparing the values obtained at the output of his invention by means of the percentage                     VZ        C            -              VZ                  R          //          C                            VZ      C        ,where VZC is the output voltage when an impedance with a capacitance only is connected to the circuit as dielectric, while VZR//C is the output voltage from the circuit with the dielectric comprising of the same capacitance connected in parallel with a resistance. The values of capacitance and resistance as calculated for wood under the conditions of the published data will now be used. After trivial calculation the results show an error in excess of 90% obtained when the method of Ahtianien is used on wood as dielectric i.e. measuring wood but ignoring the influence of resistance Rd. The invention of Ahtianien can therefore only measure a dielectric for which the resistive component is negligible and is therefore not applicable to the measurement of wood as a dielectric as was clearly shown. It is therefore of the convoluted type as defined and described above in the section under subtitle “Definition of and Comparisons between Resistive and Capacitive Sensors.” Clearly Ahtianien's method fails when used with wood as a dielectric. Athanien would typical show a capacitance almost double the value of the actual value of the capacitance contained in wood as dielectric medium which is clearly unacceptable.
Vogel [J] discloses a method by means of measuring the loss-tangent tan δ to determine moisture content. It would not be unacceptable to assume that the method presented by Vogel measures loss-tangent (tan δ) accurately and that we may discuss his method in terms of tan δ as he do claim in the title and claims of his patent. The reader is referred to consult the exact same data used for Ahtianien from the table found in Torgovnikov[C]. Upon inspection of the loss-tangent at       ρ    =          0.5      ⁡              [                  g                      cm            3                          ]              ,T=90° C. it is clear that tan δ has a maximum at about 30%. As stated above, it is not acceptable to have a single measurement correlated with two possible moisture contents as outcomes as ambiguity clearly results. Based on the cited public data, if the instrument of Vogel indicates tan δ=29, then two moisture contents will be displayed by the instrument, namely 20% m.c. and 100% m.c. An operator not informed about the present state of the wood will have no way of knowing which of the two moisture contents are the correct one. It is clear that this method and all other methods based on tan δ can only be used when the wood is either known to be very wet or very dry in advance. To make matters worse, the maximum in tan δ shifts with temperature and frequency further limiting it's use and further necessitating even more hindsight. Upon closer inspection of FIG. 5 in vogel, it is seen that indeed, Vogel constrained his measuring apparatus severely by only allowing measurements between 8-15% m.c. out of the normal 0-200% m.c. required for a full range measurement method. It must be noted in addition that the principle of Vogel is dependent on reference components in the form of an accurate 90° phase-shift and that he uses this phase shift to obtain the complex current of the dielectric resembling the loss-tangent. It must also be evident that since Vogel only measures the complex current, insufficient data prevents separation of the exact values of Cx and Rx, as loss-tangent is dependent on both of these dielectric components. This application can therefore be classified as obtaining an approximated form of the loss-tangent by measuring a property closely related but not exactly the loss-tangent tan δ.
Lundström [B] does not disclose that sinusoids are used or measured across the dielectric to be measured or phase angle is sensed. A resonance technique is used in the form of a tank circuit as the measurement principle. It also discloses that a current is measured which is then used to approximate the power loss. The power loss is related to a measurement which can isolate Rx out of the complex dielectric which also includes Cx. The description of the patent does disclose that the circuit attempts to obtain Rx independently from Cx. The method however is not capable of obtaining Cx and is in effect still dependent thereof as is strikingly evident in the manner compensations are used to eliminate the effects of Cx. The method used in this application clearly uses a method of “brute force” to attempt to get rid of Cx. The method relies on the connection of a large capacitance in parallel with the tank circuit containing the wood dielectric. It is disclosed that this larger capacitance is then used to obscure the capacitance in the dielectric in order to eliminate it's effects. It can be deduced with certainty that this method cannot obtain Cx at all. The method also discloses that the application of the device is by means of comparison i.e. a reference sample of known moisture content is first measured, then other samples are compared in reading with the reading of this reference sample. There is therefore no exact relationship to moisture content for this measurement principle, nor is there any claim their measurement is related to published moisture vs dielectric property relationships. It must be noted in passing that the “large capacitor” as used is selected of magnitude μμf. This is usually equal to pF (pico Farad). Almost all wood containing moisture content displays capacitance far in excess of 10 pF so the units and the text are contradictory in description. The author probably meant 10 mF=10 000 μF, as this would be used to force the imaginary part   1      j    ⁢                   ⁢    ω    ⁢                   ⁢          C      x      of the impedance to zero (if the frequency is chosen to be relatively low) although it is hardly an acceptable method to suppress the influences of Cx compared to a method which would calculate the influence of Cx and subtract the known influence. It is disclosed that Rx is measured or correlated with moisture but as explained above such a method cannot measure above f.s.p. The description also discloses that the measurement system is dependent on power supply variations and temperature influences and that hardware implementations need be introduced. In this regard thermisters are introduced to temperature compensate the design against thermal drifts.
Ted [A] discloses a method by which he measures resistance or reactance of which the latter can be constructed from either a capacitance or inductance. It is not disclosed in the patent that combinations of say Rx and Cx can be measured simultaneously. In fact the description indicates that there are three different methods by which each of Rx, Cx and Lx are obtained. This is then classified as a composite method unable to obtain Rx and Cx accurately when combined into a single dielectric to be measured. Ted also discloses hardware compensations necessary to eliminate power supply variations and oscillator amplitude variations. To conclude, the opening sentence in the claims states that the invention measures selectively, either Rx or Cx or Lx but not combinations thereof.
Kraxberger [M] does not disclose that his circuit measures E, but he claims he measures the impedance. If we assume that he does incorporate E to obtain an impedance measurement another question arises. It must be remembered that the impedance of a wood dielecteric is complex i.e.       Z    x    =            R      x        +                  1                  j          ⁢                                           ⁢          ω          ⁢                                           ⁢                      C            x                              .      Therefore in order to obtain the complex impedance, the phase angle between I and E must also be known. None of these items are described and it becomes clear that the method is meant to measure only the magnitude of the complex impedance. It is also clear that no phase detection of any sort is performed. The method can therefore not be used to obtain to pick out Cx and Rx from a parallel combination and obtain them accurately. It must be noted that the amplitude of the complex impedance of the wood dielectric is dependent on Rx and therefore will have detrimental influence on measurement above f.s.p as explained in above. It is also disclosed that the system can only work satisfactory if the probing cables are shielded and where the shield is driven in anti-phase to the applied signal for the purpose of eliminating the probe-cabling capacitances. This is therefore a hardware implementation to illuminate probe-cable capacitances. It is also important to note, that this application uses a single plate as a probe. It is also noteworthy that this probe is equipped with standoffs as displayed in FIG. 4. The reason for this is to eliminate the influence of conductivity and therefore Rx in order to present some form of resistive isolation and reduce currents from flowing with contact. This is in fact the attempt to eliminate the influence of Rx in the complex impedance of the wood dielectric. Isolation of probes proved unsuccessful and was investigated by James and Boone [R] who tested similar systems in great detail with mixed results. The equivalent circuit in FIG. 2 displays a bridge circuit by which only C4 can be adjusted to bring the bridge into balance. It is well known that in order to obtain both Rx and Cx from the complex dielectric, at least two components in a bridge needs to be varied. The circuit in FIG. 2 therefore establishes that the method cannot pick out Zx and Rx from a parallel combination and obtain them accurately.
Perry [O] discloses a method by which a bridge is connected to the wood complex dielectric. Perry acknowledges that the wood displays two properties namely Rx and Cx. He then correctly discloses in his description that as wood dries, Cx decreases while Rx increases. Perry then correlates exactly this dynamic with moisture content. Perry uses one conductive plate as probe to the dielectric. The invention of Perry is basically similar to Kraxberger[M]. Both uses a capacitive bridge connected to the dielectric by means of a conductive plate and the imbalance of the bridge is then correlated to the moisture content.
Bechtel [G] discloses an invention for small sample online measurement of grain-direction and not moisture content. No relevance is found.
Preikschat [H] discloses that the relative permittivity increases with increase in conductivity. As this statement is true for some instances it might not necessary be true for all condition of wood. If it is remembered that             ω      ⁢                           ⁢              R        x            ⁢              C        x              =          1              tan        ⁢                                   ⁢        δ              ,and that /tan/delta generally resembles a bell-curve w.r.t. moisture content from 0-100% James in Torgovnikov[C], and since it is known that the relative permitivity ∈r is curvilinear and monotonic but tan δ not necessarily so, establishes Rx as not necessarily monotonic which is in stark contrast with this statement. Should you have a method by which you can measure Rx and Cx accurately, there would be no need to compensate Cx for changes in Rx. Since Preikshat has to compensate Cx w.r.t changes in Rx, his method and the compensation is contained in one of the claims, he therefore most probably do not obtain Rx and Cx accurately from the complex dielectric and a resulting influence of Rx on Cx is encountered.
Walsh [K] discloses a method by which he first detects the resonant frequency of a tank circuit of which the dielectric, comprising of Rx and Cx is measured in soil samples. The variable components “120” and “122” are then used to obtain the frequency of resonance. He then utilizes the equations             W      2        =                            1                                    R              1                        ⁢                          R              2                        ⁢                          C              1                        ⁢                          C              2                                      ⁢                                   ⁢        and        ⁢                                                   ⁢                                                 ⁢                              V            2                                V            1                              =              1                  1          +                                    C              2                                      C              1                                +                                    R              1                                      R              2                                            ⁢         at this specific resonant frequency. The problem with this method is, that Rx and Cx when wood is the chosen dielectric, is extremely frequency dependent as was mentioned above and by James[P]. For the case of wood containing 100% m.c. at a temperature of 90° C., ∈r=600000 at 20 Hz and 27 at 1 MHz. In general any organic dielectric will have different moisture contents as it absorbs or loses moisture as time passes. This will demand from Walsh's method to select a different resonant frequency at every different time of measurement. This is not the case for soil and ceramics in general and Rx and Cx remains frequency independent with varying moisture content. For wood therefore Walsh's method would clearly require additional information and families of curves for each set of resonant frequency and moisture content which could have been avoided by a method fixed at a single chosen frequency. This method therefore fails to measure the severely frequency dependent dielectric of wood as the two equations presented by Walsh are not sufficient. The method of Walsh should then need to be used at 3 frequencies, with an extra equation in order to eliminate frequency. It is therefore not adequate to measure the dielectric of wood and fails the objective as described as a predefined frequency cannot be chosen and one is left to have to accept whatever the resonant frequency is Walsh's method selects. If a user demands Rx and Cx of wood at a specific frequency, Walsh's method fails as described in the text as an extra equation is needed.
Wagner [L] discloses a method for measuring the moisture content of Veneer. The application is not relevant, the method involves measuring the amplitude of the current through a detector which is then correlated to moisture content. No phase detection or voltages measured claimed or described and no separation of the components of the complex wood dielectric is evident or claimed.
Dechene [Q] discloses a method for measuring the current flowing through the capacitance of a liquid dielectric. The method was devised with objective to measure a very small capacitance in the presence of a very large conductance of a liquid. The purpose of the invention therefore is to correlate with capacitance Cx of the medium and not Rx. The operation is as follows, since the capacitive current component will be 90° shifted with the conductance current, the method revolves around introducing a phase shift of 90% to create two signals differing by this phase shift. These two signals are then used in a summation to cancel out the conductive current from the complex current obtained from the dielectric sample. This invention proposes to achieve by means of a hardware implementation to obtain and single out the current through Cx only from the complex dielectric. This invention therefore measures a quantity proportional to             i      c        =                  C        c            ⁢                        ∂                      V            x                                    ∂                      ∂            t                                ,where Vx is the voltage across the Cx.
Cox [S] and [T] disclose a method by which the voltage across a dielectric, the current through the dielectric and the phase difference between these two signals are obtained. In FIG. 5 of Cox[T], the impedance is clearly stated as meaning impedance as ohms, thereby explaining that impedance is to mean the magnitude |Zx| of the complex impedance Zx=|Zx|ejθ and not the complex impedance itself. Percentage water is clearly correlated there with the magnitude of impedance, which results in a measurement correlation with m.c. equal to that of Kraxberger although the methods differ largely. The fundamental difference is that the phase angle is explicitly used to detect water-cut, but not for calculating the complex impedance Zx. The complex impedance is therefore not obtained in this application.
To conclude, James & Boone 1982[R], in the conclusion of that publication, clearly stipulated the need that technologists and inventors should move away from measuring only the magnitude of the impedance in early 1980 and concentrate on obtaining the components of the complex dielectric. James in a report circa 1997[U], expressed the same sympathies establishing that pure capacitance was still not implemented commercially due to technical difficulties.